U.S. Pat. No. 6,708,011 (corresponding to Japanese Patent Application Publication No. 2003-015378) discloses a color image forming apparatus including a photosensitive member cartridge having four photosensitive members, a corona charger arranged around the four photosensitive members, and a cleaning device, all making up an integral unit. The photosensitive member cartridge is pulled and removed from the apparatus main body and is mounted into the apparatus main body, while a developing unit attached to each photosensitive member is detachably mountable relative to the photosensitive member cartridge.